Saturday, January 30, 2021

LEAF 12 Volt Battery Health

 Its that time of year when we are monitoring the weather report to see if road conditions warrant leaving for work 15 minutes earlier to make it on time. Its all about managing snow, sleet, ice and...your 12 volt battery. If you are a member of several LEAF groups like me, it will likely take you  less than 5 minutes to find one "car won't start" post and the culprit 95% of the time?  You guessed it.  So some ideas of keeping that battery reliable thru the Winter is something I think we all need to investigate.

Lead Acid Batteries 

12 volt battery issues during Winter didn't start with the Nissan LEAF.  I can't tell you how many times I cussed and bitched every time I couldn't get my $115 (yeah that is what I paid for it) Chevelle to start on a frigid January morning when living in Michigan. Being less than 5 miles from Lake Huron meant it wasn't a "dry" cold, it was a "feel every single degree of icy chill" cold along with that "nice" breeze. As a teen, I was lucky to have a car (although where we lived, you really didn't have much of a choice. Our town had no bus service that left town and we didn't live anywhere near town) but nowhere near the status of being able to park in the garage so it was all about my car not freezing over night while parked under the Elm tree in our yard. 

This meant at least half a dozen times a winter getting Mom's keys so I could jump my car with hers while hoping my fingers weren't permanently frostbitten during the process.  The reality is cold cars don't want to start first thing in the morning.  Now this was a 12 volt battery that was immediately topped off to a full charge right after starting. Right where lead acid wants to be; fully charged.  But if driving an EV (No, the LEAF is not the only EV with this issue) you are not afforded all the advantages you could have in the frigid fight of the Fahrenheit!

Nissan 12 Volt Management

Nissan's BMS charges the 12 volt battery on a regular basis triggered by several different events.  Starting the car is one, having the car sit for an extended period of time is another.  In none of these cases is the 12  volt battery fully charged. When 24 kwh packs were the norm, I could understand Nissan not wanting to spend a lot of electrons on topping off the 12 volt battery. So it was really all about creating an algorithm  that would boost the charge enough to keep it in the safe zone and for many of us, it works.  But the number of people who do have problems along with much larger packs suggests Nissan could be doing a better job. 

To be fair, they do warn you when the 12 volt battery is low (now why that warning doesn't trigger additional charging sessions is anyone's guess)  but like all "idiot" lights, by the time you see it, damage has already been done. According to Battery U, time under 50% SOC on a lead acid battery PERMANENTLY devalues the capacity. 

Symbol appears in upper left corner of the screen in red

The Test Part One

I park in a garage which means my 12 volt issues will be greatly mitigated simply because the battery won't get nearly as cold as one sitting outside. I also live in the Pacific Northwest 3 miles from the southern apex of Puget Sound which means pretty mild winters for the most part. 

Now because I have a Plus and a 28 mile roundtrip 4 day commute, I could easily gain enough range the night before my workweek began to cover me for the  week without any additional charging.  I did this for 4 weeks checking the battery voltage in the morning before taking off for the day.  The results were not encouraging. 

Day 1 range; 12.28 to 12.55 volts

Day 2 ranged from 12.15 to 12.41 volts

Day 3 ranged from 11.91 to 12.31 volts. 

Day 4 ranged from 11.99 to 12.21 volts

Now its obvious that the car is getting a boost from the battery during the night at least occasionally. This explains the high end voltage readings. Most of the readings were nearer to the low end of the range. Now I think with the newer LEAFs, the  12 volt gets boosted daily but was unable to capture it charging. Leaving LEAF Spy running all night is an option because it will only stay connected if the car is on which would have changed the algorithm  that controlled the 12 volt charging mechanism so I set up my Go Pro on the slowest frame rate to run all night to try to to catch charging sessions and it failed to capture anything in 4 days. When the 12 volt battery is being actively boosted and the car is not charging, the right charging light (facing the car) on the dash blinks. I will probably revisit this. 

NOTE; For anyone wondering how much power the car uses in the "on and parked" state. I split duty with my dryer plug to charge the car so am only running at 5.88 KW (240 volts, 24 amps)  LEAF Spy shows power in and out of the battery and here you see a .5 amp difference between car on, car off. Using the "PIE" formula (volts * current = power) You can see 5.22 KW of the 5.88 KW feed making it to the battery with car off.  With car on, its 5.04 KW. 


During this time, garage temps ranged from 48 to 58º and a few times, I was wondering if I should grab my boost box. 

Garage temp 51.9º 6:55 AM, car last driven 6:22 PM previous day

Luckily the car still started. I couldn't help but wonder if it would have started if parked outside when the previous overnight low was 39º?  After the car started, I decided to charge to see how long the 12 volt battery would boost.  

Lead acid needs over 14 volts to charge and LEAF Spy logs verified the 12 volt charging at 14.48 volts, just starting just 3 amps. (FYI; LEAF Spy not running the entire time so normally we would see a lot more entries in the drop to under 2 amps with each entry ~ 6 second intervals) 

But the battery only charged for 6 minutes.  FYI; I have a 12 volt battery charger that recommends 4 amp charging medium duty (cars) so 6 minutes? Yeah, barely qualifies as life support. 

Now this may come as a shock to some but there are misconceptions going around on social media including the fact that the normal voltage the LEAF 12 volt DC system runs on 13.04 volts; is enough to charge the battery. This is NOT true, not even a little tiny bit.  The battery is essentially electrically disconnected from the system. 

I then scoured my LEAF Spy logs and found the average to be around 4-5 minutes for a boost with some being as short as 2 minutes. I did see one event that went 7 minutes until LEAF Spy was shut down. Had I only known...

Test Part Two

This part of the test, I measured the voltage every morning when I got up like part one but this time, I plugged the car in immediately afterwards. I would only be charging for ~ 75 minutes so SOC was still quite low (under 50% most of the time)  Since I was charging every day, there was no sense in breaking out day one, day two, etc. so I took 8 measurements (2 weeks worth)

Range; 12.18-12.71 volts. (ok, the 12.71 volts probably should have been tossed out as 2nd highest was only 12.48 volts) 

Wow! so charging every day definitely helps but not nearly as much as I had hoped. I will say that the garage was colder as low as 46.8º and the highest during this time was only 53º. Unlikely significant...

NOTE: Although my car enjoys the pampered life at home, she is just another car at work braving the elements in an uncovered lot for 10½ hours a day.

Living On The Edge

All this made me wonder "Just how close am I to the flame?"  So I went out, checked the battery and it was its customary range at 12.12 volts with the garage at 57.4º. I disconnected the battery entirely from the car and it read 12.30 volts.  I knew that my trip computer would be reset when I disconnected the battery so I turned on the car just long enough to get my LEAF Spy readings for the day before doing all this.  But a .2 volt drop from the system was an interesting data point. 

NOTE; I don't have telematics (Nissan Connect, CARWINGS or whatever its called nowadays) but I do have Wi Fi. Its my guess that Wi Fi is not active when the car is off so shouldn't make a difference. 

So I hooked up the charger. Voltage went to 14.40 volts so a bit lower than the LEAF system. And...

Well, not looking super good (to say the least) 

It did move to 50% in less than 3 minutes. Another 13 minutes to 75%. The time to 100% will be of less value because when the charger senses the voltage starting to rise, it will cut back the current and I have no real way of knowing how much. Either way, I am charging 50-100% faster than the LEAF would be so its pretty obvious that most of the boosts are coming nowhere near bringing the battery as high as 50% charged. Now for Lithium, that would be awesome but Lead Acid? 50% ensures an early death. 

I let the charger run for 40 minutes disconnecting when the charge voltage hit 14.52 volts which was near when the current would likely start to drop. After reconnecting the battery, I waited 5 minutes and checked it. 12.33 volts.  Don't know how much good it did but I sure feel a lot better about it. 

FYI; Temps expected to be below freezing tonight 😉


Naturally a few days after I publish this, Elon responded. He is usually pretty good about that ;) 


  1. My 2018 SV 12V battery charges every day for around 5 minutes. I have a workshop in my garage and I hear the relay for the dc/dc converter kick in and see the right hand dash light come on. I purchased a 1200W PSW inverter to power my furnace and fridge from the 12V Leaf battery during a power outage. The inverter digital display reads 14.4V when I turn on the car and power a load from the inverter. I'll have to get my VM ready to measure the 12V battery next time the dc/dc converter kicks in. Hopefully get a before and after reading.

    1. As I suspected. Still the 5 mins of charge is insufficient to bring the SOC to 75% which I consider the minimum needed for 12 volt longevity. As far as the charging voltage, its 14.48 volts consistently which is another red flag.

      Lead Acid charges at its maximum supplied current until it senses the voltage starting to rise, then it dials back the current to maintain the voltage in the correct range. This NEVER happens on the LEAF which makes sense as this doesn't happen until the battery is well over 80% SOC.

      FYI; According to Battery U, extended periods below 50% SOC in lead acid PERMANENTLY devalues the battery's capacity.

    2. I measured 14.53 volts today while it was charging (for only around 5 minutes). At rest voltage after charging & letting it normalize is 12.54 volts. Based on this chart it is around 60% charged.

    3. Nothing wrong with that but I took 24 measurements and only saw one reading in that range. So your reading is not typical especially during colder weather but then again, 12 volt battery issues during Summer are fairly rare where I live.